Precured tire tread strips are manufactured on a large scale for use in retreading tires. During the manufacturing process a rubber composition is molded into the form of a strip of tread of finite length, e.g. 12 feet, and having a desired rib and groove pattern in one surface, and the molded strip is vulcanized in the mold under high pressure and temperature to give a tough long-wearing tread strip. Subsequently the strip is cut into appropriate lengths each of which is used to retread a tire by wrapping the length around a prepared tire carcass and then bonding the two together.
It is often desirable to permanently join the end of one piece of precured tread strip to the end of another such piece. This may also arise from the production of pieces of relatively short length during the manufacturing operation as a result of cutting out flawed sections of longer pieces. Such short pieces are not usable as such for retreading operations but when joined together end-to-end the resulting integral piece is suitable for retreading purposes. Also it is sometimes desirable to join together the standard pieces to make a still longer piece for use on automatic tread machines.
Splicing or joining pieces of precured tread strips can be carried out with known equipment which applies clamping pressure in directions normal to the tread faces of two tread pieces arranged in end-to-end relationship. A rubber-base vulcanizable bonding material previously inserted between the two ends bonds the ends together under the influence of heat which is applied during the clamping operation.
The present invention contemplates a splicing or joining technique which positively presses the ends of the two tread pieces together under high pressure by applying forces to the end portions in the plane of the pieces, while at the same time applying the heat required for the bonding step. The apparatus in its broadest form includes two mold elements each of which has a ribbed surface complementary to the grooved surface of the respective tread strip, two clamping elements each cooperating with one of the mold elements to clamp a tread strip therebetween, power means for effecting relative movement between the clamped tread strips such that the ends of the strips are abutted and forced tightly together, and means for applying heat to the abutted ends.